用于连接不同表的SQL

Question

I have the following tables :

I want to write a Select Statment that show the following result

I Tried to Join/ Union/Union All the two table but I dont get the desird output. Can anyone help me with it?

Answer 1

select
 'group_a' as groupname
, max( case classname when 'C123' then group_a else null end)  as c123
, max( case classname when 'C456' then group_a else null end)  as c456
from table1
union all
select
 'group_b' as groupname
, max( case classname when 'C123' then group_b else null end)  as c123
, max( case classname when 'C456' then group_b else null end)  as c456
from table1
union all
select
 'group_d' as groupname
, max( case classname when 'C123' then group_d else null end)  as c123
, max( case classname when 'C456' then group_d else null end)  as c456
from table1
union all
select
 'group_e' as groupname
, max( case classname when 'C123' then group_e else null end)  as c123
, max( case classname when 'C456' then group_e else null end)  as c456
from table1